Method for open-end rotor spinning

ABSTRACT

It is the object of the invention to propose a method for open-end rotor spinning, wherein the formation of cover yarn, in particular the so-called “belly bands”, is at least appreciably reduced.  
     In accordance with the invention, the fiber flow exiting a fiber guide channel has a directional component in the direction of rotation of the rotor, while the yarn leg ( 3 ) extending from the draw-off nozzle to the rotor groove, is curved opposite the direction of rotation of the rotor, at least near the rotor groove ( 1 ), during the spinning process. The creation of this direction of curvature of the yarn leg ( 3 ) takes place during the piecing process.

[0001] The invention relates to a method for open-end rotor spinning,wherein the fibers to be spun are conveyed via a fiber guide channelinto the rotor, are collected in its rotor groove of the largestinterior diameter, are tied while being twisted into the yarn end in thearea of a so-called tie-in zone by means of the rotor rotation and aredrawn off as finished yarn through a draw-off nozzle, which is arrangedcentered and substantially on one level with the rotor groove.

[0002] The development of rotor spinning goes back a very long time,wherein the industrial use of this method only started on a larger scalein the sixties. A multitude of inventions was created not only inperipheral areas, i.e. from the sliver feed, the opening up intoindividual fibers and feeding of the individual fibers to the spinningrotor, as well as the drawing-off and winding-up of the yarn, but alsoin the core area of yarn formation, i.e. inside the rotor, only a smallportion of which has entered into the present-day, very efficientautomatic rotor spinning machines, which produce a yarn of high quality.

[0003] All methods have essentially in common that fibers from a sliver,which have been opened into individual fibers by means of an openingcylinder, are conducted together by means of a vacuum air flow to therotor and are conveyed against a circumferential wall by means of theair flow and/or centrifugal force. As a rule, the shape of the innerrotor wall permits the collection of these fibers by forming an almostclosed fiber ring. These collected fibers are continuously tied-up intoa yarn end, wherein the yarn performs a true twist with every revolutionof the rotor. The yarn rotation wanders opposite the yarn draw-offdirection from the draw-off nozzle in the direction toward the yarncollection and, by the twisting of the doubled yarn, makes itscontinuous spinning on the open yarn end possible. The area where thispiecing of the fibers to the yarn end takes place, is located betweenthe detachment point of the yarn being created from the rotor wall, andthe transition from the twisted yarn into the untwisted small sliver. Itis called the tie-in zone.

[0004] Normally a yarn end for a piecing, which is fed into the rotor bythe draw-off nozzle, is taken along in the direction of the rotorrotation by the air flow formed by the rotor rotation, at the latestwhen reaching the rotor groove. This curvature of the yarn end in thedirection of rotor rotation is then maintained during the entirespinning process.

[0005] As can be seen from JP-OS 49-54 639, a malfunction can be causedby intensive soiling in the rotor, large bundlings of fibers, or theloss of the vacuum supply. The flipping of the curvature of the yarn endcaused by this is quite undesirable, as stated in this Japaneselaid-open document, since the yarn created in the course of this is saidto show considerable disadvantages in respect to strength and eveness incomparison with a yarn, whose yarn end is curved in the direction of therotor rotation. To prevent this flipping of the curvature opposite therotor rotation direction, it is proposed in JP-OS 49-54 639 to arrangeappropriate yarn contact elements on the draw-off nozzle and the rotorbottom, which are intended to stabilize the desired direction ofcurvature.

[0006] Within the scope of the further developments of the open-endspinning methods it was possible to definitely improve the processes, sothat it is normally possible to avoid large collections of fibers,soiling or the failure of a vacuum. Accordingly, modern open-endspinning machine in principle are operated without additional aids formaintaining the curvature of the yarn end in the direction of rotationof the rotor.

[0007] A rotor spinning arrangement is described in “Breakspinning”,report of the Sherley Institute, Manchester, England, 1968, pages 76 to79, wherein a funnel-shaped false twist element is arranged inside ofthe actual spinning rotor, which itself has the shape of a pan. Thisfalse twist element extends directly up to the fiber collection surfaceof the rotor. The rotor and the false twist element are separatelyseated and can also be separately driven. This means that the falsetwist element can be arranged in a stationary manner, as well as beingdriven in the direction of the rotor rotation, or opposite the directionof rotor rotation. Openings are arranged in the area of the collectingsurface, by means of which a suction flow is created because of thecentrifugal force of the rotor rotation. The fibers are fed in theradial direction on the collecting surface, which has the approximateshape of a cylinder surface. The yarn is drawn off through the rotorshaft, i.e. at the location opposite the fiber feed-in.

[0008] As described there, the relative direction of rotation of theyarn leg can be changed in relation to the rotor rotation as a functionof the direction of rotation of the false twist arrangement. It isstated in conclusion that this relative rotation direction of the yarnleg clearly affects the yarn quality. Thus, in the positive direction,i.e. with the yarn leg running faster than the rotor, the yarn qualityis said to be better by approximately 18% than with the oppositelydirected relative speed of the yarn leg in relation to the rotorrotation.

[0009] A problem, which reduces the employment options of the rotor yarnproduced on modern open-end rotor spinning machines, which otherwise hasvery even and good physical textile properties, resides in the formationof cover yarn, the so-called “belly bands”, which are wound inalternating directions of rotation either loosely, but partially verytightly, around the yarn periphery. The yarn structure, or the fiberorientation and fiber stretching, suffers because of this, with theresult that the range of application of open-end rotor yarns becomeslimited.

[0010] It is therefore the object of the invention to propose a methodwhich limits the creation of cover yarn at least noticeably.

[0011] In accordance with the invention, this object is attained bymeans of the characteristics of claim 1.

[0012] The invention will be advantageously further developed by meansof the characteristics of claims 2 to 5.

[0013] The method in accordance with the invention is based on theknowledge that, with a curvature direction of the yarn end in thedirection of rotation of the rotor, fibers which, coming from the fiberslide face, directly reach the tie-in zone of the yarn end are initiallytied to the twisting yarn in a direction which is opposite the normalyarn twisting direction, wherein in the course of the continued draw-offof the yarn, along with a simultaneous twisting thereof around its ownaxis, the direction of twisting of this fiber changes to the main yarntwisting direction. In those cases in particular in which the fiberreaches the tie-in zone first with its end located at the front in thedirection of rotation of the rotor, several locally concentrated wrapscan be created when the direction of rotation is changed. The yarn isconstricted at this point with the result, that the yarn is uneven andthe twist propagation is braked, which results in a loss of strength ofthe yarn in turn.

[0014] The setting in accordance with the invention of the curvature ofthe yarn opposite the direction of rotation of the rotor results insingle fibers, which reach the yarn end in the tie-in zone, areimmediately tied on, or in, in the normal twisting direction of the yarnand therefore do not cause any interference with the yarn production,nor a lack of quality arising therefrom.

[0015] Because of the detachment of the yarn end from the rotor groove,the angular speed of the detachment point, or of the tie-in zone,differs from the angular speed of the rotor. In the case of a curvatureof the yarn end in the direction of rotation of the rotor, the angularspeed of the tie-in zone is greater than that of the rotor, the tie-inzone runs ahead of the rotor. In the case of the present invention, witha curvature of the yarn end opposite the direction of rotation of therotor, the tie-in zone trails behind the rotor. Because of this trailingof the tie-in zone, the fibers are drawn out of the rotor groove underan increased tensile stress. This results in additional stretching,which leads to an improved orientation of the fibers and makes possiblean increased use of the strength of the fiber substance. In contrast toyarn which was produced with a leading tie-in zone, yarn produced inthis way has a distinctive yarn core of stretched fibers.

[0016] The fact that with a trailing tie-in zone the fibers are tied tothe yarn end with the same orientation with which they were conductedthrough the fiber guide channel to the rotor, also has an advantageouseffect on the yarn structure. Here, the tangential alignment of thefiber flow in the direction of rotation of the rotor also assures thestretching of the fibers, because the inner surface of the rotor, i.e.the fiber slide surface, has a greater speed than the fiber flowimpinging on it. This continuous maintenance of the stretching directionadditionally furthers the stretched deposition of the fibers in the yarnstructure.

[0017] By feeding the fiber flow onto a fiber slide surface, the fiberflow exiting the fiber guide channel is prevented from directly hittingthe tie-in zone or the yarn end.

[0018] In accordance with the invention it is necessary to establish thetrailing of the tie-in zone already in the course of the piecingprocedure, in particular for obtaining an even yarn quality during theentire spinning process.

[0019] If no appropriate precautions are taken during the piecingprocedure, leading of the tie-in zone automatically occurs because ofthe air flow which rotates along with the rotor. This orientation of theyarn leg is additionally aided by the rotation flow being createdbecause of the tangential junction of the fiber guide channel and of thevacuum prevailing in the rotor housing. In the course of introducing theyarn end it is accordingly necessary to see to it that an oppositecurvature is being formed.

[0020] This can be accomplished for one by generating a rotary flowopposite the direction of rotation of the rotor while the rotor stillstands still, or does not yet rotate very fast, which acts on the yarnend being conducted from the draw-off nozzle to the rotor groove andwhich impresses the desired curvature on the yarn end. During this timethe suction of the rotor housing can be maintained, since it aids theactive air supply in the direction opposite to the rotation, which is incontrast to the passive suction of the fiber guide channel.

[0021] After the yarn end with the direction of curvature opposite thedirection of rotation of the rotor has reached the rotor groove, thisstate is stabilized with the increasing number of rotor revolutions andtherefore also the centrifugal force, and then remains as stable as inthe state with a leading tie-in zone. In this connection the fact shouldbe taken into consideration that the interferences mentioned in theprior art, which could cause a curvature change, are no longer relevantbecause of the command of the spinning process, as well as because ofkeeping the rotor clean.

[0022] The means used for generating the rotary flow can also be usedfor the so-called rotor flushing if it is necessary to remove the fiberswhich have reached the rotor in the course of a so-called fiber tuftequalization prior to the actual piecing (for example, see DE 197 09 747A1).

[0023] Alternatively there is also the possibility of turning the rotoropposite its normal direction of rotation prior to the piecing procedurein order to cause in this way a deposition of the yarn end in thisdirection of rotation, which is opposite to the direction of rotationduring its operation. In this case the suction of the rotor housingshould be switched off in order not to endanger the desired depositionof the yarn leg by the suction flow, which causes a rotary flow in thedirection of rotation of the rotor because of the tangential orientationof the fiber guide channel.

[0024] Following this, the rotor should be switched into the operatingdirection of rotation, but this process must not take place so abruptlythat the direction of curvature of the yarn end flips again. Here, too,a stable curvature of the yarn end opposite the direction of rotation ofthe rotor is assured after the rotor has been run up. In addition, aslight twisting open of the yarn end during the rotation of the rotoropposite the normal operating direction also is advantageous for thepiecing process. This yarn end, which has been opened further, is thenbetter suited for a piecing process.

[0025] Besides the variations for creating the direction of curvature ofthe yarn end opposite the direction of rotation of the rotor describedup to now, there are alternatively options of forming a fiber ring priorto introducing the yarn end into the rotor, or to switch the fiber flowinto full strength after the yarn end has reach the rotor groove and therotor has the number of rotor revolutions necessary for the process.

[0026] A further possibility for achieving the curvature in accordancewith the invention of the yarn leg, or of the trailing thereof, consistsin generating a yarn loop during the piecing procedure. In the course ofthis the yarn end is conveyed in the customary manner through the yarndraw-off tube into the rotor. Thereafter, a suction flow is generated ina radially spaced apart suction channel, while the spinning vacuum isshut off. Because of this the yarn end wanders from the draw-off nozzleinto this suction channel. The feed length is regulated by thecontrolled feeding of the yarn through the yarn draw-off tube. At theend of feeding, the yarn end is clamped in the suction channel.Thereafter, a spinning vacuum is again generated and the rotor isstarted. Because of a continued return feed of the yarn, a larger sizeloop is formed between the draw-off tube and the suction channel. Theair rotation caused by the rotor rotation pulls the loop in thedirection of rotation of the rotor. After the loop has been sufficientlyaligned in this way, the clamping is released, so that the yarn end canbe deposited in the rotor groove opposite the direction of rotation ofthe rotor. Thereafter yarn draw-off is very rapidly accelerated, and thepreviously stepped yarn feed is restarted. In the process the yarn endis tied to the fibers. As in the already mentioned cases, the curvatureof the yarn leg is stabilized by means of the centrifugal force thenapplied. With this process variation it is only necessary to see to itthat no early feeding of fibers into the spinning rotor takes place inorder to prevent the flipping of the yarn leg into the other directionof rotation in a phase which has not yet been stabilized by centrifugalforce.

[0027] Stopping the yarn feed prior to the piecing process is not tiedto a particular method here. For example, the fed-in fiber tuft can bedeflected as long as is required by means of suction air directlydownstream of the feed table. On the other hand, it is also possible todisplace this point of the fiber flow deflection into the area of thefiber feed channel (for example, see DE 31 18 382 A1). It is onlyimportant that the fiber feed is completely stopped in the piecing phasein which the curvature of the yarn is formed.

[0028] The invention will be explained in greater detail in what followsby means of exemplary embodiments. The associated drawings show in

[0029]FIGS. 1a and 1 b, various variations of the generation of coveryarn in the course of spinning with a leading tie-in zone,

[0030]FIGS. 2a and 2 b, various variations of the generation of coveryarn in the course of spinning with a trailing tie-in zone,

[0031]FIG. 3, a channel plate adapter with air outlet openings arrangedaround the draw-off nozzle for creating a rotating air flow,

[0032]FIG. 4, a lateral view of FIG. 3, showing the rotor in addition,

[0033]FIGS. 5a to 5 c, various movement phases of the rotor during thepiecing process for creating a trailing tie-in zone,

[0034]FIG. 6, the chronological sequence of the winding speed of therotor in the phases in accordance with FIGS. 5a to 5 c,

[0035]FIG. 7, a front view of the essential spinning elements of a rotorspinning arrangement,

[0036]FIG. 8, a lateral view of the working element of a spinning box,

[0037]FIG. 9, a sequence of the yarn return for creating a trailingtie-in zone,

[0038]FIG. 10, a lateral view of the working elements of a spinning box,partially modified for the execution of the sequence represented in FIG.9,

[0039]FIG. 11, a lateral view essentially showing the spinning chamber,as well as a piecing cart arranged in front of the spinning box,respectively in partial views, and

[0040]FIG. 12, a front view of the essential spinning elements of arotor spinning arrangement, with a suction device for the temporarydeflection of the sliver.

[0041] The phases of the tie-in of a single fiber 4 during spinning witha leading tie-zone, i.e. alignment of the yarn leg 3 in the direction ofrotation of the rotor, are represented in FIG. 1a, wherein this singlefiber 4 reaches the rotor groove 1 from the fiber slide surface 2 at atime when its front end is grasped in the tie-in zone 5 of the yarn leg3 (phase 1). It can be easily seen that the fiber twist direction in theyarn leg 3 is Z-wire. In contrast to this, the fiber 4, whose tip hasbeen grasped, is initially wound in S-turns around the yarn surface, ascan be seen in phase 2. In the course of the further yarn draw-offV_(L), the tip of the fiber 4 nears the point at which further portionsof the fiber 4 are wound around the yarn surface at that instant. Achange in the direction of twist from S to Z takes place in phase 4, inthe course of which several concentrated wraps can be created. Thesewraps as a whole tie the yarn together and form so-called belly bands,which can be in the way in the later processing stage and as a wholereduce the quality of th yarn. In phase 5 it can also be seen that theremainder of the fiber 4 is wound up in a Z-twist, i.e. the sametwisting as the remaining yarn.

[0042] If the end of the fiber 4 is initially spun onto the tie-in zone5 (FIG. 1b). the following sequence results: in phase 1, the fiber meetsthe tie-in zone and is grasped in phase 2 by the yarn leg 3 in the areaof the tie-in zone 5. The fiber tip of the fiber 4 follows the directionof rotation TG of the yarn around its own axis and is drawn off in aZ-twist until it is completely drawn out of the rotor groove 1 and iswound around the yarn core (phases 3 to 5), while the fiber end is woundin an S-twist around the fiber core. The fiber is not solidly bound intothe yarn core, but rests loosely around the yarn surface.

[0043] But in FIGS. 2a and 2 b it is shown how the tie-in of anindividual fiber 4 to the yarn leg 3 takes place within the tie-in zone5 if spinning is performed with a trailing tie-in zone 5, i.e. with acurvature of the yarn leg opposite the direction of rotation of therotor.

[0044]FIG. 2a shows in phases 1 to 5 how a fiber 4, coming from thefiber slide surface 2, reaches the tie-in zone 5 with its tip and iswound around the yarn surface. It can be seen here that from the startthe fiber 4 is tied to the yarn leg 3 in the same twisting direction asall other fibers. Only the pitch of the twist differs slightly from theother fibers. The same occurs in accordance with FIG. 2b if the fiberinitially meets the tie-in zone 5 with its end.

[0045] Therefore the yarns produced in this manner do no longer containfibers with a twisting direction different from the normal yarn twistingdirection. Above all, wraps are no longer created because of a change inthe twisting direction, which would affect the yarn quality, andtherefore the possibilities of use of the spun yarn.

[0046] Since in the course of a normal piecing process a curvature inthe direction of the rotation of the rotor inevitably results because ofthe air flow rotating along with the rotor, it is necessary to takemeasures for creating the opposite direction of curvature of the yarnleg.

[0047] A first variation for the creating in accordance with theinvention of a trailing tie-in zone is represented in FIGS. 3 and 4 andwill be described in greater detail in what follows.

[0048] A channel plate adapter 10, which can be inserted into a channelplate, supports a draw-off nozzle 11 with a nozzle opening 13, as wellas radial notches 12, known per se, which are used for increasing thespinning dependability. Air outlets 14 which, as indicated by the arrows15, have a tangential direction component, terminate radially outsidethe draw-off nozzle 11. Furthermore, a fiber guide channel terminatesaxially and radially offset, of which the mouth opening 16′ can be seen.The arrow 17 indicates that this fiber guide channel, too, has atangential orientation, which can be seen more clearly in FIG. 7. Thetangential direction components 15 and 17 are oppositely directed.

[0049] The air outlets 14 are supplied via an annular channel 19, whichitself is connected to a compressed air source, not represented, via acompressed air supply device 20 and a valve 21.

[0050] The compressed air supply device 20 can also be connected to aso-called piecing aid which, by means of an air feed, causes a rotorflushing of the rotor prior to the actual piecing process after fibershad been pre-fed for fiber tuft equalization which are not to be madeavailable for the piecing process. A device as described in DE 197 09747 A1, for example, would be suitable for this. Therefore it is notnecessary to address further details here.

[0051] As can be seen in FIG. 4, the annular channel 19 is created by anappropriate shaping of the base body of the channel plate adapter 10,together with a cap 22 which has the air outlets 14. The nozzle opening13 terminates in a yarn draw-off tube 18, through which the yarn end isintroduced for piecing and, after piecing, is continuously drawn offduring the spinning process.

[0052] The tangential direction of the fiber flow indicated by 17, whichis caused by the orientation of the fiber guide channel 16, correspondsto the direction of rotation of the rotor during its operation. Incontrast to this, the air rotation direction (see arrows 15), which canbe achieved by feeding compressed air through the air outlets 14, isdirected opposite the direction of rotation of the rotor. The air supplyis limited to a first piecing phase by means of the valve 21, duringwhich the yarn end is introduced into the rotor through the yarndraw-off tube 18 and the nozzle opening 13. When the yarn end reachesthe rotor groove 1, this rotating air flow must assure that the yarn endis curved opposite the direction of rotation of the rotor. After rotorrevolutions which apply sufficient centrifugal forces to the yarn endhave been reached, flipping of the direction of deposit of the yarn endis no longer to be expected. The further spinning process can be solidlyperformed with a trailing tie-in zone.

[0053] A further variation for obtaining an appropriate curvature of theyarn leg 3 is represented in FIGS. 5a to 5 c and 6.

[0054]FIG. 5a shows a rotor 6, whose direction of rotation, or angularspeed TR<0, i.e. has been set opposite the direction of rotation of therotor during its operation. The yarn leg 3, introduced into the rotor 6through the draw-off nozzle 7, is accordingly deflected into thisdirection of rotation of the rotor when it reaches the rotor groove. Inthis case the vacuum supply to the rotor housing should be turned off,in order not to create an opposite rotational flow because of thetangential termination of the fiber guide channel.

[0055]FIG. 5b shows the stopped rotor (TR=0) while the yarn leg 3remains in the position it has reached in accordance with FIG. 3a. FIG.5c then shows the run-up of the rotor in the direction of rotationduring its operation (TR<0). In the course of this the direction ofcurvature of the yarn leg 3 is maintained. The acceleration must belimited in such a way that flipping of the direction of curvature of theyarn leg 3 into the direction of rotation of the rotor is prevented.

[0056]FIG. 6 shows the sequence of movements of the rotor in the firstphase of the piecing process, in which the curve 8 shows a variation inwhich the direction of rotation of the rotor is switched directly fromreverse running to forward running. But the curve 9 shown in dashedlines shows a dwell time )t of the stopped rotor. These sequences ofmovement are primarily a function of the drive mechanisms used.Different variations of such drive mechanisms will be discussed ingreater detail below.

[0057] In FIG. 7 it is shown how a sliver 28, which is guided between aclamping spot between a feed roller 26 and a clamping table 27, comesinto the area of the teeth of an opening cylinder 24, which rotates inthe interior of an opening cylinder housing 23. When the sliver leavesthe clamping spot between the feed roller 26 and the clamping table 27,it is opened into individual fibers by means of the opening cylinder 24,and dirt particles are removed through a dirt removal opening 25. Thefibers, which have been combed out by means of the opening cylinder 24,then reach a fiber guide channel 16, through which they are aspirated bymeans of the vacuum prevailing in the rotor housing and are furtheraccelerated. By means of the increasing taper of the fiber guide channel16, the fiber flow 29 is accelerated and the fibers are furtherstretched in the process. The fiber guide channel 16 opens at a fiberguide channel opening 16′ into the rotor in such a way that the fibersmeet the fiber slide surface 2 of the rotor 6 tangentially and arefurther accelerated by the rapidly rotating rotor 6 and are stretched.

[0058] Because of the trailing tie-in zone, the direction of orientationof the fibers is not again changed even in the course of the yarnformation, because the yarn end is oriented toward the mouth 16′ of thefiber guide channel 16, as can be seen in FIG. 7, and therefore thefiber tips are first tied to the yarn end. In contrast to this, with aleading tie-in zone the fiber ends are first tied to the yarn end.

[0059]FIG. 8 shows the components 30 of a spinning box which are part ofthe spinning process. The rotor shaft 6′ of the rotor 6 is radiallyseated in a support ring bearing 40, i.e. between the nips of supportrings 41, 42 arranged in pairs. An axial bearing 43 of the rotor isarranged at the end of the rotor shaft 6′, which radially fixes therotor in place in both directions. This can be a magnetic radial rotorbearing here, such as described and represented in DE 198 19 766 A1, forexample.

[0060] The rotor 6 is arranged in a rotor housing 33, which is connectedvia a suction line 46 with a vacuum source 47, so that a permanentspinning vacuum prevails in the rotor housing 33. This spinning vacuumprimarily provides that the fibers are aspirated through the fiber guidechannel 16 into the rotor 6.

[0061] A channel plate 32 is arranged in a pivotable cover element 34and supports a channel plate adapter 31. The cover element 34 can bepivoted around the pivot shaft 35, by means of which the rotor housing33 is opened. In this state the rotor 6 can be cleaned or removed, forexample. Accordingly, this cover element 34 is opened prior to thepiecing process by a service unit, which customarily can be displacedalong the rotor spinning machine in order to perform the cleaning of therotor.

[0062] The opening cylinder 25 is also seated by means of a bearingbracket 39 in the pivotable cover element 34 and is driven via a wharve38 by means of a tangential belt 37. A driveshaft 36 drives the feedroller 26 by means of a worm drive, not represented here. On its frontend, the feed roller has a crown 26′, on which a drive mechanism of thepiecing cart can be placed in order to be able to perform the driving ofthe feed roller 36, controlled by the piecing cart, during the piecingprocess.

[0063] The rotor 6 is driven via its rotor shaft 6′ by means of atangential belt 48, which during its operation is maintained infrictional contact with the rotor shaft 6′ by means of a pressure roller49. Customarily this tangential belt extends over the entire length ofthe rotor spinning machine, so that it drives all rotors on a side ofthe machine.

[0064] A drive motor 44 is additionally provided which, by means of afriction wheel 45, acts on one of the support rings 41 as soon as it hasbeen brought into contact with it. For this purpose this drive mechanismis arranged to be moved toward or away from the support ring 41, asindicated by the two-headed arrow, by means of a lifting device, notrepresented. This additional drive mechanism 44, 45 is employed duringthe first phase of the piecing process in order to create anoppositely-extending direction of rotation of the rotor when the contactroller 49 is lifted off, and with it also the tangential belt 48, suchas explained in the course of the description of FIGS. 5a to 5 c. Sincethis drive mechanism does not have to provide high numbers ofrevolutions, it can be of very small size.

[0065] It would also be alternatively conceivable to arrange the drivemechanism on the service unit and to introduce it into the spinning boxthrough the rotatable cover element 34.

[0066] The reversal of the direction of rotation of the rotor could alsobe accomplished in that a second tangential belt is extended over theentire length of the machine, whose direction of movement is oppositethat of the tangential belt 48. Then this second tangential belt wouldbe temporarily pressed against the rotor shaft 6′ by means of a secondcontact roller during the first phase of the piecing process.

[0067] Alternatively to the generation of the opposite direction ofrotation it would also be conceivable to employ individual drivemechanisms for rotors, whose direction of rotation can be easilyreversed. Such an individual drive mechanism is described by way ofexample in DE 198 19 767 A1. It is therefore not necessary to provide adetailed description of such a drive mechanism at this point.

[0068] A further method for forming the curvature of the yarn 3 oppositeto direction of rotation of the rotor is represented in six phases inFIG. 9. The first phase shows the customary feeding of the yarn throughthe yarn draw-off tube into the spinning chamber, or the rotor, by meansof the effects of the vacuum (spinning vacuum) prevailing in thespinning chamber.

[0069] In a second phase the yarn 3 is deflected around the draw-offnozzle 7 into a suction channel 51 (see FIGS. 10 and 11). This takesplace in that the spinning vacuum is switched off and an auxiliary airflow is generated in the suction channel 51. After the end of the yarn 3has been aspirated sufficiently far into the suction channel 51, it isclamped by means of a clamping device 50 (only schematically indicatedin FIG. 9) in the suction channel 51 (phase 3).

[0070] In phase 4, additional yarn is fed in through the yarn draw-offtube while the spinning vacuum is again applied and the rotor is startedin its customary running direction. By means of this a loop is formed inthe yarn 3, which extends in the direction of the rotor rotation.

[0071] In phase 5 the clamping by the clamping device 50 is releasedafter sufficient yarn has been introduced into the rotor 6, so that thedeposition of the yarn end 3 opposite the direction of rotation of therotor is assured.

[0072] Phase 6 shows that the yarn end coming out of the suction channel51 is deposited in the rotor groove 1.

[0073] It is shown in phase 7 that in the course of the continued run-upof the rotor the yarn is drawn-off the rotor as rapidly as possible, inparticular to avoid a larger overlap between the yarn and the furtherfed-in fibers. While no fibers must be supplied to the rotor in phases 1to 6 in order to avoid the flipping of the yarn end in the direction ofrotation of the rotor, the full fiber flow must be available suddenly inphase 7 in order to have a sufficient amount of fibers available in therotor collecting groove 1, which can be tied to the yarn end. It isassured in this way that the cross section and the solidity of theso-called piecer approach that of the normal yarn as closely aspossible.

[0074]FIG. 10 shows a suction/clamping device 53 in the suction channel51. If it is possible to set the fed-in length of the yarn by means of ayarn feeding device 60 (FIG. 11) exactly in such a way that an exactlypredetermined length of the yarn is aspirated in the suction channel, itis merely necessary to provide a clamping device. A more detailedrepresentation of such a clamping device has been omitted here, sinceonly the blade is omitted there.

[0075] But if the yarn is to be cut to size in the suction channel 51,it is necessary to provide a suction/clamping device 53. An actuatingswitch 54 is coupled with the suction/clamping device 53 and can switchthe latter on and off. As shown in FIG. 11 in connection with this, anactuating rod 55 is arranged on the piecing cart 58, which can act onthe actuating switch 54 in a controlled manner. The piecing cart 58moreover contains a suction tube 56, which can be connected by means ofa sealing element 57 to the suction channel 51. By means of this theauxiliary air flow can be generated, chronologically controlled, in thesuction channel 51 for forming the yarn loop in the end.

[0076] A support of the piecing cart 58 can also be seen and has aroller which supports it along the spinning machine against therespective boxes in the course of the displacement of the piecing cart58.

[0077] The switching processes, as well as the supply of the auxiliaryair flow, can also be performed by the spinning station itself. The samevacuum source which provides the spinning vacuum can be used for this.In this case in particular the cutting to size of the yarn 3 by means ofthe clamping/cutting device 52 is advantageous.

[0078] A variation is represented in FIG. 12, which shows a possibilityfor deflecting the fiber flow. A suction connector 61 is connected via avalve 63 with a suction air source 62. This suction air source 62 canagain be arranged on the piecing cart or on the spinning station itself.If suction is applied to the suction connector 61, the sliver fed in bymeans of the feed roller 26 over the clamping table is kept away fromthe fittings of the opening cylinder 24 and is therefore not furthercombed out. After a short running time of the opening cylinder with asupply of sliver, no fibers are present anymore on the opening cylinder24. The shut-off of the suction air at the suction connector 61 by meansof the valve 63 takes place early enough so that, when the phase 7 fromFIG. 9 has been reached, the fiber flow is fully available again in therotor. However, other arrangements of the suction connector 61 along therunning direction of the opening cylinder 24, or even in the fiber guidechannel 16, are also conceivable.

1. A method for open-end rotor spinning, wherein the fibers to be spunare conveyed via a fiber guide channel (16) into the rotor (6), arecollected in its rotor groove (1) of the largest interior diameter, aretied while being twisted into the yarn end in the area of a so-calledtie-in zone (5) by means of the rotor rotation and are drawn off asfinished yarn through a draw-off nozzle (7, 11), which is arrangedcentered and substantially on one level with the rotor groove (1),wherein the fiber flow exiting from a fiber guide channel (16) has adirectional component in the direction of rotation of the rotor, andwherein the yarn leg (3) extending from the draw-off nozzle (7, 11) tothe rotor groove (1) is curved, at least in the vicinity of the rotorgroove (1), opposite the direction of rotation of the rotor during thespinning process.
 2. The method in accordance with claim 1,characterized in that the fiber flow is essentially fed to a fiber slidesurface (2) located between the rotor opening and the rotor groove (1).3. The method in accordance with claim 1 or 2, characterized in that thedirection of curvature of the yarn leg (3) is created during the piecingprocess.
 4. The method in accordance with claim 3, characterized in thatin a first phase of the piecing process a rotary flow directedtangentially opposite the direction of rotation of the rotor during itsoperation is caused to act on the yarn end introduced into the rotor (6)for piecing, which flow is sufficient for creating the intendeddirection of curvature of the yarn leg.
 5. The method in accordance withclaim 3, characterized in that in a first phase of the piecing processthe rotor (6) is initially driven opposite the direction of rotation ofthe rotor during its operation in such a way that the intended directionof curvature of the yarn leg (3) occurs, and that the direction ofrotation of the rotor during its operation does not exceed an angularacceleration T which could lead to the flipping of the direction ofcurvature.
 6. The method in accordance with claim 3, characterized inthat after its exit from the yarn draw-off tube, the yarn returnedthrough the yarn draw-off tube (18) by means of the application ofsuction to the spinning chamber is aspirated into a radially spacedapart suction channel (51) by means of an auxiliary suction flowprevailing there and is fixed in place in this suction channel,thereafter the spinning vacuum is applied again and the rotor (6) isstarted, because of which a yarn loop extending in the rotor is alignedin the direction of rotation of the rotor and, by means of thesubsequent release of the yarn end (3), the latter is deposited in therotor groove (1) in such a way that it is oriented opposite thedirection of rotation of the rotor.
 7. The method in accordance withclaim 6, characterized in that following the fixation of the yarn end(3) in the suction channel (51), yarn is continued to be fed through theyarn draw-off tube (18) until such a yarn loop has been formed whichfollows the rotor (6) which has again been put into operation.
 8. Themethod in accordance with claim 6 or 7, characterized in that the yarnend (3) is cut to size in the suction channel (51), and the cut-to-sizeyarn end is fixed in place.
 9. The method in accordance with one ofclaims 1 to 8, characterized in that during the orientation phase of theyarn end (3) the rotor (6) is kept free of fibers, and the feeding offiber suddenly takes place only after the direction of curvature of theyarn end (3) in the rotor groove (1) has been sufficiently stabilized bymeans of centrifugal force.